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• FFMPEG C++ API audio/video sync, video is longer [closed]

  11 mai 2023, par Gábor Gombor

  I create a video from frames in C++ with a given FPS and supply it to FFMPEG API. I record from an Unreal engine viewport and feed FFMPEG with the images. In this interval I have also an audio track in FLAC which I want sync with the video. When the music ends, I close the video and merge them, but the final video has sync problems, the video is a little bit longer than the audio, so I will have an increasing delay. For example I record 0:55 secs, the audio is ok=same length, but the video from frames will be 0:56 secs.

  


  I think the following code is problematic :

  


  bool MyVideoExporter::writeFrame(OutputStream* oStream, AVFrame* frame, int& framePTS)
{
    auto* packet = oStream->pkt->pkt;
    auto* codecContext = oStream->enc->codecContext;

    frame->pts = framePTS;
    frame->pkt_dts = frame->pts;

    auto ret = avcodec_send_frame(codecContext, frame);
    if (ret >= 0) {
        auto retVal = 0;
        while (retVal >= 0) {
            retVal = avcodec_receive_packet(codecContext, packet);
            if (retVal == AVERROR(EAGAIN) || retVal == AVERROR_EOF) break;
            else if (retVal < 0) {
                return false;
            }

            // rescale to audio, usually 1/44100
            av_packet_rescale_ts(packet, m_audiotimestamp, oStream->st->time_base);
            // rescale to FPS, usually 1/30 or 1/60
            av_packet_rescale_ts(packet, codecContext->time_base, oStream->st->time_base);

            packet->stream_index = oStream->st->index;

            retVal = av_interleaved_write_frame(m_avFormatContext.avFormatContext, packet);
            if (retVal < 0) {
                return false;
            }

            framePTS++;
        }

        return retVal == AVERROR_EOF;
    }

    return false;
}



  


  Any idea what is wrong ?

  


  I tried change the order of av_packet_rescale_ts lines or move the frame increase code to another places, but getting far worse results.

  


• how to check the number of duplicated frame for video 1sec ( about 30frames ) from video start and want to apply this for mpdecimate

  20 octobre 2018, par cool jobs

  How to check the number of duplicated frame for video 1sec ( about 30frames ) from video beginning point ? I want to apply this for mpdecimate with audio. Some videos have three duplicated frames, some videos - 15 duplicated frame, some videos have 19 duplicated frames.. so it looks I need a variable or math operator in ffmpeg as expression.

  1. some video have duplicated frames at beginning point , but it is
     not same always the number of duplicated frames.
  2. if get back variable which is for the number of duplicated frames
     from step-1 then split and trim apply mpdecimate with audio as
     much as step-1 variable returned, finally do concatenate each other.

  Is this possible with -filter_complex for one line ffmpeg command ?

• FFMPEG merging audio and video to get resulting video

  26 septembre 2016, par King

  I need to merge audio and video using ffmpeg so that, it should result in a video with the same duration as of audio.

  I have tried 2 commands for that requirement in my linux terminal. Both the commands work for a few of the input videos ; but for some other input_videos, they produce output same as the input video, the audio doesn’t get merged.

  The commands, I have tried are -

  ffmpeg -i wonders.mp4 -i Carefull.mp3 -c copy testvid.mp4

  and

  ffmpeg -i wonders.mp4 -i Carefull.mp3 -strict -2 testvid.mp4

  and

  ffmpeg -i video.mp4 -i audio.wav -c:v copy -c:a aac -strict
  experimental output.mp4

  and these are my input videos -

  1. samplevid.mp4

  https://vid.me/z44E

  duration - 28 seconds

  size - 1.1 MB

  status - working

  And

  2. wonders.mp4

  https://vid.me/gyyB

  duration - 97 seconds

  size - 96 MB

  status - not working

  I have observed that the large size (more than 2MB) of the input video is probably the issue.

  But, still I want the fix.